1. Field of the Invention
The present invention relates to a bearing which is adapted for use at an intersection of a column and a cross rail in a machine tool such as boring or planing machine or at an intersection of vertical and horizontal shafts in a general conveyor so as to support and slide a heavy-weight object, and more particularly it relates to a cross-linear bearing unit capable of achieving accurate positioning of a slide member by linearly moving the same in both vertical and horizontal directions.
2. Description of the Prior Art
A tool rest disposed on a column and a cross rail in a machine tool generally receives, during a machining operation, great forces exerted in reverse, downward and horizontal directions in addition to the extremely large weight of its own. Since such forces are exerted at a point spaced apart from the tool rest plate, a large reversal force is applied to the column shaft. Therefore, it has been customary heretofore to use a slide guide surface in the guide region for elimination of the resultant problem. In the case of a rolling guide, a large-diameter column shaft is employed with a bearing of a corresponding large load capacity such as described in the U.S. Pat. Nos. 3,003,828 or 3,341,262. However, incorporating the bearing of this type into a machine causes an increase in the production cost due to the necessity of using an expensive hardened steel plate, and moreover it is extremely difficult to attain a high accuracy particularly in the case where a plurality of such bearings are disposed at horizontal and vertical positions.